A common practice in the field of power conversion is to use switching power supplies to convert DC voltage of one level to a DC voltage at a second level. A circuit topology that is well suited for this purpose is the full bridge converter. A common ZVS topology for a prior art full bridge converter is a phase-shifted full bridge. In other words, the drive signal that is used to control the full bridge converter comprises phase shifted signals.
An example of one such circuit is described in detail in a Texas Instruments (formerly Unitrode Corp.) generated application note U-136A entitled “Phase Shifted Zero Voltage Transition Design Considerations and the UC3875 PWM Controller,” published in May 1997, and presently available from Texas Instruments, Inc. The phase shifted full bridge described therein requires a special function chip to translate a DC control voltage into a phase shifted signal for driving one side of the full bridge switches.
As will be realized, special function chips typically cost more to purchase and are single sourced as compared to integrated circuits that are widely used in the industry. Further, if changes are required in the phase shifting control signal to output algorithm for a similar but different application, a new special function chip may be required. Also phase shifting circuitry is typically more complicated and susceptible to noise creating jitter than PWM signal generating circuitry.
It would thus be desirable, where product cost, multiple sourcing and simplified circuitry are among the design considerations, to be able to use an industry standard existing integrated circuit as a signal source for generating a duration controlled set of output pulses. Such a chip may be used in conjunction with a further circuit, which may advantageously utilize discrete components for generating a pair of constant width drive signals and a further pair of PWM drive signals to operate a full bridge converter power supply.